There are many new chemo-optical sensing devices that are read optically.
Many of these sensors involve a chemosensor component that is photometrically interrogated by an electro-optical component. In these sensors, the electro-optical component may measure optical changes at the chemosensor component such as absorption changes at ultraviolet and/or visible wavelengths (e.g. color changes), fluorescent and/or phosphorescent emissions, and optical scattering properties. When fluorescent reagents are utilized a fluorescent substance is excited by stimulus light at a stimulus wavelength, and one or more substances in the chemosensor component absorbs this stimulus light and emits light of a longer wavelength.
Such sensors may have enzymatic components in their chemosensor component, such as the enzymatic biosensors described in U.S. patent application Ser. No. 12/358,140, hereinafter the '140 application, filed 22 Jan. 2009, and entitled ENZYMATIC BIOSENSORS WITH ENHANCED ACTIVITY RETENTION FOR DETECTION OF ORGANIC COMPOUNDS, which is hereby incorporated herein by reference.
For example, photoluminescence (PL), a generic term for both fluorescence and phosphorescence, may be employed for sensing by exciting a sample and directly looking for the PL spectrum of the analyte or by indirectly observing changes in the PL of another species affected by the analyte. Optical enzymatic biosensors typically use an indirect mechanism whereby the products of the reaction modify the PL efficiency of nearby dye molecules. For example, conversion of toluene by a monooxygenase consumes dissolved oxygen in the proximity of an oxygen-sensitive ruthenium-based dye thereby altering the dye's PL efficiency and lifetime. Higher analyte levels result in higher reaction rates and thus depleted oxygen levels, reducing oxygen alters phosphorescent emission of the ruthenium dye under constant excitation power.
Each chemosensor or biosensor typically has an optode for coupling light to and from optical fibers to a sensor component. Chemosensors of particular interest herein are biosensors in that they incorporate a biological component in the sensor component. The biological component may be prepared of living organisms embedded in other materials, or may be made of isolated enzymes and/or antibodies combined with other materials.
Many prior sensors have a one-to-one relationship between the electro-optical component and the chemosensor component. These prior sensors typically have an interrogation light source coupled directly or through an optical fiber to the chemosensor component, and an electro-optical detector component coupled directly or through an optical fiber to the chemosensor component.
For example, consider the prior-art sensing device 100 illustrated in FIG. 1; this device has a chemosensor element 102, such as those known in the art or described in the '140 application that undergoes a change in fluorescent properties with analyte concentrations in its environment. A stimulus light source 104 provides light at a stimulus wavelength suitable for stimulating fluorescence in chemosensor element 102. Stimulus light source 104 may be a laser, may be a light-emitting diode, or may be another light source as known in the art. Light from light source 104 passes to chemosensor element 102, and stimulates fluorescent light emissions at a fluorescence wavelength that is typically longer than the stimulus wavelength. In embodiments where light source 104 emits significant light at the fluorescence wavelength, a wavelength-selective device 106, such as a high-pass optical filter, is interposed between light source 104 and chemosensor element 102 to block light at the fluorescence wavelength.
In this device, fluorescent light emitted by chemosensor element 102 passes through a second wavelength-selective device 108, typically a filter, that blocks light at the stimulus wavelength while passing light at the fluorescence wavelength. Light passed by wavelength-selective device 108 enters a photodetector 110. A processing device 112 uses photodetector 110 to make readings of light at the fluorescent wavelength, applies any necessary correction factors, and provides readings of analyte concentrations.
Many chemosensor elements 102 known in the art provide faint fluorescent light at some analyte levels of interest, in part because analyte levels of interest may be quite low. For example, it is desirable to detect substances such as the highly toxic organophosphate Sarin at levels that are below those that cause harm to most mammals. In order to accurately measure such faint fluorescent light, sensitive photodetectors 110 may be required, including such photodetectors as avalanche photodiodes and photomultiplier tubes. Such sensitive photodetectors may be rather costly.